430 DR. S. F. HARMER ON THE 



as Crenothrix Kuhniana { = C. polyspora Colin). A scientific 

 Commission was appointed to investigate the matter ; and the 

 memoir cited was the result. The Bacteria in question, which 

 grow associated in long filaments, flourish in the presence of iron 

 in solution in the water. Under these conditions, and when pro- 

 vided with the requisite organic matter, they deposit the iron, in 

 an insoluble form, in the sheath which forms the outer part of 

 the filament. Where they are present in sufiicient numbers 

 they then flake off the inside of the pipes in masses which pass 

 into the circulation and are delivered with the water into the 

 domestic supply, where they cause great annoyance. This result 

 may become a serious calamity by rendering the water extremely 

 unpleasant for domestic use, and completely unusable for many 

 industrial purposes (De Vries, 90, p. 9). The remains of animals 

 and plants which have died in the pipes are said to provide 

 the organic matter which is required by the Iron-Bacteria. The 

 growth of these organisms is commoidy associated with the 

 formation of a hard deposit on the inner sides of the pipes; 

 and this may give rise to serious trouble by reducing the flow 

 of water. 



I am indebted to my colleague Mr. A. Gepp, of the Botanical 

 Department of the British Museum, for calling my attention to 

 some of the special points of interest in connexion with Iron- 

 Bacteria. A good general account of the subject may be found 

 in De Vries' memoir and in the works of Lafa.r (98, 04), while 

 an extensive bibliography is given on pp. 90-92 of one of 

 Kemna's memoirs (05). One of the special pointsof interest in 

 this connexion is the theory, first brought forward byWinogradsky, 

 that the Iron-Bacteria take up iron in solution in the ferrous state 

 and obtain their energy by oxidizing it to the ferric state, which 

 appears in the form of iron-rust deposited in the sheaths of the 

 filaments. The theory has been criticised by some of the more 

 recent workers, as by Molisch, who claims to have kept Iron- 

 Bacteria for several generations in iron-free solutions. It has 

 been suggested that the deposit of iron-rust in the sheath of 

 Crenothrix and other forms is of the same general nature as the 

 appearance of silica in the cell-wall of a Diatom : and that it has 

 not the physiological significance which was attributed to it by 

 Winogradsky. But whatever the nature of the process may be, 

 the peculiar property possessed by these Bacteria of depositing 

 iron in the ferric state is a matter of the utmost practical 

 importance to Water Engineers. 



The removal of the pipe-fauna, or the establishment of condi- 

 tions under which a fauna of this kind cannot effect an entrance, 

 appears to be of great importance in preventing the growth of 

 Iron-Bacteria. As De Viies pointed out, these organisms require 

 organic matter, which is supplied to them in abundance, in un- 

 filtered water, by the disintegration of the constituents of the 

 pipe-fauna. Au instructive case, which appears to be of this 

 nature, is discussed by Kemna in his account of the troubles 



